Plate and Shell type welded plate heat exchangers are previously known, which are composed of a plate pack formed by heat exchange plates and a shell surrounding it, functioning as a pressure vessel. The core of the heat exchanger is usually formed by a plate pack composed of circular heat exchange plates, where the plates have been welded tightly together at openings therein and/or at the perimeters of the plates. A primary circuit of the heat exchanger is formed between the openings in the plates and a secondary circuit between connections of the shell surrounding the plate pack, so that a primary side flow medium flows in every other plate space and a secondary side flow medium in every other plate space. In heat exchangers of this type the flow connections of the pack side are usually placed in the ends of the heat exchanger and the flow connections of the shell side in the shell. Due to the small openings in the heat exchange plates the flow pattern of the pack side is not the best possible, as a large part of the flow strives to pass through the middle part of the heat exchange plate. A disadvantage of heat exchangers of the Plate and Shell type is also that separate flow guides are needed on the shell side, which are used to prevent bypass flow between the plate pack and the shell. Construction of the flow guides to be completely tight has been discovered to be a difficult task. In order to obtain a sufficient tightness, the flow guides are manufactured from flexible materials, such as rubber or corresponding materials. A Plate and Shell type plate heat exchanger is described for example in patent publication WO 2008/046952.
A so-called Raucell type welded plate heat exchanger is also previously known. A constructive disadvantage with the Raucell type heat exchangers is, especially when performing at high pressures, the lack of a solid shell structure manufactured for example from pressure vessel steel. Because the stacked plates of the plate pack are welded together by their outer edges, this structure makes up the outer shell of the plate heat exchanger, which shell also functions as a pressure vessel. Therefore Raucell type plate heat exchangers are best suited for low pressures. Pipes, which have partly been split in the longitudinal direction, have been welded to the sides of the plate pack as connections for the plate pack. These split pipes function as bypass manifolds for the heat exchanger. Due to the small size of the bypass manifolds for heat exchange mediums, the heat exchange surface of the heat exchange plates is also in this type of exchanger not utilised fully. A Raucell type plate heat exchanger is described for example in patent publication WO 89/00671.
Patent publication WO2012/089927 shows a welded plate heat exchanger, where all the heat exchange mediums are led to the welded circular plate pack from its outer perimeters and removed via the outer perimeters along flow channels, the cross-sections of which have the shape of a section of a circular ring, which flow channels are formed between the outer surface of the plate pack, the inner surface of the outer shell, the radial baffle plates arranged on the outer surface of the plate pack and the ends of the heat exchanger. The structure presented in the application is advantageous as a pressure vessel, but the heat exchange occurs according to a cross-flow principle, whereby it is not possible to obtain so-called cross temperatures, which are possible with counter-flow exchangers. An advantage of the construction shown in the application is a completely welded structure, whereby rubber-sealed flow guides are not needed. The costs of the structure according to the application however grow significantly if it is desired to reduce the corrosion risk of the heat exchanger, because the outer shell of the heat exchanger must thus be manufactured from the same material as the heat exchange plates.